This application is based on Japanese Patent Application No. 2001-195204 filed on Jun. 27, 2001 the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an engine control system for a vehicle. The system has an idling stop and automatic restart feature.
2. Description of Related Art
JP-A-58-166165 discloses an engine control system that engages a lock-up clutch of a torque converter and stops fuel supply to the engine when the vehicle in a deceleration and vehicle speed is reduced gradually. As a result, the engine is kept in rotation by directly connecting a crankshaft of the engine and an automatic transmission. It is possible to improve fuel economy.
In this case, it is normal to prevent engine stall by releasing the lock-up clutch and restarting fuel supply when the engine speed is reduced to a predetermined value higher than an idling engine speed in a state of cutting fuel.
JP-A-8-189395 has proposed an engine automatic starting and stopping system for reducing an amount of fuel consumption more than the above-described conventional technology by carrying out a control of cutting fuel while bringing a clutch into a connected state during a time period of establishing an automatic stopping condition of an engine even in the case in which a fuel cut control condition is not established and automatically stopping the engine by releasing the clutch when a clutch releasing condition is established during the time period of establishing the automatic stopping condition of the engine.
According to the engine automatic starting and stopping system, the engine is automatically stopped in running and therefore, when there is used a brake apparatus for carrying out assistance with negative pressure of an intake pipe of the engine as a power source, operability of the brake is deteriorated in running when the engine is being stopped.
With respect to the problem, when there is used a way of thinking of JP-A-58-30438/1983, negative pressure of the brake apparatus can be ensured without operating an electric negative pressure pump by detecting booster negative pressure of the brake apparatus and ensuring the brake negative pressure by restarting the engine when the negative pressure becomes equal to or smaller than a predetermined value.
However, according to the method, there is a time lag in restarting the engine and therefore, there is a case in which booster negative pressure sufficient for operating the brake cannot be ensured in rapid braking operation while stopping the engine in running.
It is an object of the present invention to provide an automatic engine stop and start system that is capable of supplying sufficient negative pressure for a brake device.
It is another object of the present invention to provide an automatic engine stop and start system that is capable of restarting the engine before negative pressure is decreased below a predetermined threshold.
According to an aspect of exemplary embodiment of the present invention, an automatic engine stop and start system has negative pressure detecting means for detecting a negative pressure for assisting a brake booster, braking operation detecting means for detecting a braking operation of a driver, and an engine controller for automatically stopping or starting the engine under establishment of a predetermined condition of the engine based on an input signal. The engine controller automatically starts the engine when it is determined that there is carried out a predetermined braking operation for bringing about, as a result, a situation in which the booster negative pressure is estimated to be smaller than a predetermined threshold based on the booster negative pressure and the braking operation.
That is, according to the constitution, the combination of the booster negative pressure and the braking operation is checked with previously stored memory information, it is determined whether the combination is accompanied by a concern of bringing about a reduction in the booster negative pressure effecting adverse influence on the braking operation and when there is the concern, the engine is restarted. Thereby, even when the booster negative pressure is provided with a value sufficiently withstanding a certain kind of the braking operation, in the case in which there is a possibility of effecting adverse influence on the braking operation by carrying out the predetermined braking operation (for example, rapid braking or high speed repeated braking), the engine is restarted and therefore, the engine can be restarted before the booster negative pressure is reduced as a result of the predetermined braking operation. As a result, without awaiting for delay time for restarting the engine, which is brought about when the engine is restarted by simply monitoring the booster negative pressure and when needed (when a reduction in the booster negative pressure needs to restart the engine), the engine can swiftly be restarted before the booster negative pressure is actually reduced and a deterioration in the braking operation can be prevented.
According to an aspect of exemplary embodiment of the present invention, a controller automatically start the engine when there is carried out an operation in which a brake depressing amount is equal to or larger than a predetermined value as the predetermined braking operation under a situation in which the booster negative pressure is equal to or smaller than a predetermined value. That is, under the situation in which the booster negative pressure is reduced to some degree, the engine is restarted with respect to the brake depressing operation having a deep depression significantly reducing the booster negative pressure. Therefore, even when the brake depressing amount is increased, a drawback by delay in restarting the engine can be resolved.
The controller may automatically start the engine when there is carried out an operation in which a rate of changing a brake depressing amount is equal to or larger than a predetermined value as the predetermined braking operation under a situation in which the booster negative pressure is equal to or smaller than a predetermined value. Thereby, there can be resolved occurrence of a failure in assisting the braking operation caused by braking operation for bringing about a rapid reduction in the booster negative pressure such as rapid braking or pumping braking significantly consuming the booster negative pressure under a state in which the booster negative pressure is proximate to an engine restarting limit.
The controller may automatically start the engine when there is carried out an operation in which an accumulated change amount of a brake depressing amount during an immediately proximate predetermined time period is equal to or larger than a predetermined value as the predetermined braking operation under a situation in which the booster negative pressure is equal to or smaller than a predetermined value.
That is, the accumulated amount is brought into a close positive correlated relationship with an amount of reducing the booster negative pressure and therefore, when the accumulated change amount of the brake depressing amount significantly consuming the booster negative pressure is large in the state in which the booster negative pressure is proximate to the engine restarting limit, by restarting the engine with respect to the braking operation, swift engine restarting can be realized and a drawback caused by a delay in restarting the engine can be resolved.
The controller may estimate the booster negative pressure when the brake depressing amount is made to be smaller than a current value thereof by a predetermined amount from the current booster negative pressure and the current brake depressing amount. The controller may start the engine when the estimated booster negative pressure is smaller than the predetermined threshold.
That is, according to the constitution, in the pumping operation of the brake repeating to depress the brake and relieve the brake, the booster negative pressure in stopping the engine is mostly consumed and the driver feels a strange feeling in depressing the brake. Hence, when the engine is restarted by detecting a reduction in the booster negative pressure in relieving the brake, the strange feeling in depressing the brake thereafter can be resolved swiftly.
According to an aspect of exemplary embodiment of the present invention, an automatic engine stop and start system has negative pressure detecting means for detecting a negative pressure of a negative pressure source generated by an engine or an apparatus driven by the engine and supplied to a brake booster for assisting a braking operation, master cylinder pressure detecting means for detecting a pressure of a brake master cylinder, braking operation detecting means for detecting the braking operation of a driver, and a controller for automatically stopping or starting the engine under establishment of a predetermined condition of the engine based on an input signal. The controller automatically starts the engine when it is determined that there is carried out a predetermined braking operation for bringing about. As a result, a situation in which the booster negative pressure is estimated to be smaller than a predetermined threshold based on the negative pressure of the negative source, the pressure of the brake master cylinder and the braking operation.
The constitution is preferable to a system that does not have a booster negative pressure detecting sensor. According to the constitution, before stopping the engine, the booster negative pressure is estimated by the negative pressure of the negative pressure source (for example, negative pressure at an intake pipe (also referred to as intake negative pressure)), the brake operating state and the hydraulic pressure of the master cylinder. Further, there is calculated an amount of consuming the booster negative pressure by the braking operation in stopping the engine thereafter from the estimated value of the booster negative pressure, thereby, the booster negative pressure in stopping the engine can be estimated. For example, the amount of consuming the booster negative pressure is estimated based on an amount of changing the brake depressing amount in stopping the engine. The booster negative pressure in stopping the engine is estimated from the amount and the booster negative pressure immediately before stopping the engine.
The braking operation detecting means may comprise a brake depressing amount sensor.
The system may further include vehicle speed detecting means for detecting a vehicle speed. The controller may adjust the predetermined threshold in accordance with the vehicle speed. That is, the smaller the vehicle speed, the smaller the braking force necessary for the braking operation and therefore, when the predetermined threshold is changed to provide a positive correlated relationship with the vehicle speed, fuel cost can be promoted by restraining to restart the engine when the vehicle speed is small.
According to an aspect of exemplary embodiment of the present invention, an automatic engine stop and start system has a brake system having a brake booster for assisting a braking operation of a driver by using a negative pressure generated by an engine or an apparatus driven by the engine, and a controller for automatically stopping or starting the engine under establishment of a predetermined condition of the engine based on an input signal. The system further comprises downward road detecting means for detecting that a vehicle runs on a downward road. The controller prohibits the engine from being stopped in running on the downward road.
That is, when the vehicle is running on the downward road, braking force necessary for decelerating the vehicle becomes larger than that in running on a flat road. Therefore, according to the brake negative pressure sufficient for operating the brake, the booster negative pressure is consumed more than in the case of running on the flat road. Hence, on the downward road, by prohibiting to stop the engine (signifying to restart the engine when the engine is stopped), the booster negative pressure is ensured firmly and sufficiently and a drawback in the braking operation in running on the downward road caused by a delay in restarting the engine can be prevented. Further, xe2x80x9cprohibit to stop the enginexe2x80x9d according to the invention includes engine restarting when the engine is stopped.
The downward road detecting means may determine the downward road when a detected inclination of the vehicle is larger than a predetermined inclination threshold. Thereby, downhill (downward road) is determined by the inclination of the vehicle and therefore, the downhill can firmly be determined.
The downward road detecting means may detect the downward road based on a detected running acceleration and a detected brake depressing amount.
That is, in comparing the flat road and the downward road, even with the same braking force, the deceleration degree of the vehicle becomes smaller in the case of the downward road. Further, in the case of a steep downward road, even when the brake is operated, there is a case of accelerating the vehicle. According to the constitution, based on the above-described fact, the downward road is detected by the amount of depressing the brake and a rate of changing the vehicle speed and therefore, a vehicle inclination sensor is not needed and the constitution can be simplified.
The system may further comprise vehicle speed detecting means for detecting a vehicle speed. The controller predominantly prohibits the automatic stopping of the engine when the vehicle speed falls in a predetermined range after restarting the engine in running the vehicle. That is, when automatic stopping of the engine is prohibited during a time period after restarting the engine in running the vehicle for ensuring the brake negative pressure until the vehicle is stopped, frequent stopping and restarting of the engine is prevented and drive feeling can be promoted.
The system may further comprise hydraulic pressure controlling means capable of controlling a brake hydraulic pressure, wherein the controller generates a braking force by directly controlling the brake hydraulic pressure by instructing the brake hydraulic pressure controlling means when information with regard to a failure in starting the engine is inputted after instructing to start the engine.
Further, the information with regard to the failure in starting the engine can be determined, for example, by the fact that the booster negative pressure is equal to or smaller than a predetermined value after elapse of a predetermined time period from instructing to restart the engine. That is, according to the constitution, when the engine fails to restart by some cause although the engine is instructed to restart, in the case of carrying out the braking operation, the vehicle is firmly stopped by directly controlling the brake hydraulic pressure and therefore, reliability in braking can further be promoted. Further, in controlling the brake hydraulic pressure, there can be driven a hydraulic actuator used in ABS, traction control, brake assisting or the like.